for example. or even signify installed/not-installed with colors if that ever gets implemented..

to atleast have some indicator wether you have or don't have the package would speed up the process of installing packages because you don't have to check if you have the opt-depends installed(i don't think anybody remembers every package they have installed.)

but this is low-prio and devs can decide if they want to add this or not(obviously they could anyway since they hold the source :P)

Well, my line of thinking on it is this: optdepends are displayed upon installation to inform the user of added functionality they can add. If it's already installed, there's no need to inform, and so the optdepends are just additional spam that doesn't need to be shown. Full optdepends could be shown for pacman -Qi.FS#12708 may or may not be related, depending on your views.

Perhaps make it configurable which way it would display it? I agree that displaying installed or not installed for optdepends would be better than the current behavior, but I think better yet would be not at all. I guess it's a matter of taste.